System of speed begulation and control of induction motors



H. A. LAYCOCK. SYSTEM OF SPEED'REGULATION AND CONTROL OF INDUCTION MOTORS.

APPucAnbN mgn AUG.8.1919- 1,408,21 1. Patented Feb. 28, 1922.

Inventor: Harr JLLa gcocK,

His flttorne g.

- sistances l4. and 14:. For the sake of illustration, the motors A. and B are shown as being connected to rolls 11 and 11".

15 and means for regulating the amount of the resistances 14 and 14 in the secondary circuits of the motors A and B, and as illustrated, comprise induction motors having primary windings, which are adapted to be connected to the distribution circuit 3. Rotatable contact members 16 andltl are operatively connected to the rotors of the motors 15 and 15 and are adapted to engage taps of the resistance 14 and 14 The connections between the primary windings oi": the induction motors 15 and 15 and the distribution circuit 3 are controlled by means of the contactors l7 and 18 contactors l7 and 18 and balance relays 19* and 19*.

Direct current generators 20 and 520", which are shown as magnet-s, are mechanically connected to the induction motors A. and 1B, and are electrically connected through adjustable resistances 22 and 22" to coils 21 and 21 of the balance relays 19 and 1 The generators 20 and 20* are designed to generate voltages which vary directly with their speeds. The opposing coils '25? and 25* of the relays l9 and 19 are adap ed to be connected to one phase of the distribution circuit 3 when the switches 10 and 10* are closed.

l llien the motors and B are operating at their normal speeds, the voltages applied to the coils 211"- and 21? of such values that the forces exerted by these relays just bal ance the forces exerted by opposing coils 25.

Circuits for energizing the operating coils of the contactors l7 and 18 and contactors 1? and 18' are adapted to be completed to a source of current 23 through switches 24 and 2 2 contacts of the balance relays l9 and 19". 1

.30 and 3%? represent eiectromagnetically controlled friction b'ffililis for the motors 15 I and 15". These brakes are adapted to be ap plied at all times, except when current is being supplied to motors, and the purpose thereoi is to bring the motors to a stop quickly when the circuits of the motors are opened.

The operation oi the system, as at present understood, is as 'follows:

Let itbe assumed that the speed or the turbine is adjusted so that the frequency of the current supplied to the distribution circuit 3 by the generator 1 is a predetermined value and that the excitation of the generator 1 is regulated so that the voltage of the distribution system is also a predetermined value. Let it be assumed {M80 that the switches 10 and 10 and the switches 24; and 24? are closed and the motors A and B are running at their normal speeds.

denote resistance varying Under such COIlLuvlOIlS the opposing coils of the balance relay 19 and 19 just balance each other and occupy the positions shown in the drawing. If the speed of one of the motors, for example motor A, decreases, the voltage of the magneto 20 also decreases so that the force exerted by the coil exceeds that exerted by coil 21.

" Consequently the balance relay 19 is operated in a clockwise direction and closes the circuit for the energizing coil of contactor 18, whereupon the contactor 18 is closed and completes a circuit for the motor 15 so as to rotate the contact member l6 in a clockwise direction and thereby exclude portions of the resistance 14 from the secondary circuit of the induction motor A. The motor speed will accordingly increase and restore the balanced relation between the two coils of the relay 19 If the speed of the motor increases above its normal value it is evident that the balance relay 19 is oper ated in a counter-clockwise direction and closes the circuit for the energizing coil of the contactor 17* which, in turn, operates to close a circuit for the motor 1.5 to rotate the contact member 16 in a counter-clockwise direction to insert portions of the resistance it in the secondary circuit of the motor A. The speed of the motor B is held constant in a similar manner by means of the balance relay 19'. lit will be evident that normal speeds of the motors A. and B can be readily adjusted to any desired value by varying the resistance 22* and 22 From the forgoing it is evident that the speed of each motor can be automatically maintained constant at value.

Let it now he assumed that it is desired to decrease the speeds of all motors connected to the distribution circuit 3 a certain percent, say 10 of their normal speeds. This is accomplished by changing-the setting'of the governor 6, so as to decrease the speed of the generator 1 to a value such that the frequency of the current supplied by the genorator 1 to thedistribution circuit 3 is reduced to 90% or its normal value, and by regulating the resistance voltage generated at the new speed to 9(l% of its normal value. it is to be understood, however, that my invention is not limited to the particular means shown in the drawing for varying the frequency and the voltage. Since the voltage supplied to the coils 25 and 25* is reduced 10%, the motors 15 and 15" are operated in the manner above described to insert resistances in the secondary circuits of the motors A and B, todecrease the speeds thereof to values such that the voltages generated by the magnetos 20 and 20 are decreased 10%. Since the voltages of these magnetos 26 and E20 vary directly with the speeds thereof, it is evident that the speeds any predetermined 9 so as to reduce the i of the motors A and B are automatically decreased the same per cent as the voltages of th magnetos 20 and 20".

Since the frequency of the current supplied to the motors is also varied the same per cent as the speeds of the motors, it follows that the relations between the actual speeds and synchronous speeds of the motors are not changed, that is the slip of each motor remains constant when the frequency is changed. Consequently, the eiiiciencies thereof remain approximately constant. For example, let it be assumed that the normal synchronous speed of motor A is 1800 R. P. M. and its normal speed at cycles is 1700 R. P. M. If the frequency is reduced 10% that is, to 54 cycles and the voltage a corresponding per cent, the new snychronous speed is 1,620 B. P. M. and the new speed produced by the'regulating 'means is 1,530 R. P. M; Therefore, the relation between the normal speed and the synchronous speed in both cases is the same, that is 1700 divided by 1800 is equal to 1530 divided by v1620. It will be evidental'so that the new speeds of the motors will be maintained constant by the speed'regulating means as long as the new frequency and voltage of the generator remain constant.

While I have herein shown and described one modification and application of my invention, I do not desire to be limited to the exact arrangement shown and described but seek to cover in the appended claims all those modifications and applications Which come within the true spirit and scope of my invention.

What I claim as new. and desire to secure by Letters Patent of the United States is:

1. In combination, a plurality of induction motors having phase wound secondary windings, a variable resistance in the secondary circuit of eachmotor, a source of electrical energy connected to the primary windlngs resistance in the secondary circuit of the motor with which it is associated so that the speed thereof is changed the same per cent as said electrical condition when the latter is changed.

2. lln combination, a plurality of induction motors having phase wound secondary windings, a variable resistance in the secondary circuit of each motor, a source of electrical energy connected to the primary windings of-said motors, means for arbitrarily regulating said source to change an electrical condition of the energy supplied to said motors. and speed regulating means to said ei-ecti condition of the energy supplied by said source, each of said regulating means heing arranged to automatically vary the resistance in the secondary circuit of the motor with which it is associated so that the speed of the motor is maintained constant at a predetermined value when said electrical condition of the source remains constant and so that the speed thereof is changed the same per cent as the'electrical condition when the latter is changed.

3. In combination, a plurality of induction motors having phase wound secondary windings, a variable. resistance in the secondary circuit of each motor, a source of electrical energy connected to the primary windings of said motors, means for arbitrarily regulating said source to change the voltage thereof, and speed regulating means for each motor responsive to the voltage of said source for automatically varying the resistance in the secondary circuit of thecmotor with which it is associated so that the speed thereof is changed the same per cent as the voltage when the latter is changed.

4. In combination, a plurality of induction motors having phase wound secondary windings, a variable resistance in the secondary circuit of each motor, a source of electrical energy connected to the primary windings of said motors, means for arbitrarily regulating said source to change the voltage thereof, and speed regulating means for each motor responsive to the voltage of said source, each of said regulating means being arranged to automatically vary the resistance in the secondary circuit of the motor with which it is associated so that the speed of the motor is maintained constant at a predetermined value when the voltage of, the source remains constant and so that the speed thereof is changed the same per cent as the voltage when the latter is changed.

5. In combination, a plurality of induc- 11 tion motors having phase wound secondary windings, .a variable resistance in the secondary circuit of each motor, a source of electrical energy connected to theprimary windings of said motors, means for arbitrarily regulating said source to change the frequency of the current and the voltage supplied thereby to said motors, and speed regulating means associated with each motor and responsive to the voltage of said source for automatically varying the resistance in the secondary circuit of the motor with which it is associat d, so that the same percentage vchange in the speeds of all the motors is produced when the voltage is changed.

6. lin combination, ,a plurality of induction motors having phase wound secondary windings, variable resistance in the sec- Cir ondary circuit of each motor. a source of electrical energy connected to the primary windings of said motors, .a generator driven by each motor, means for arbitrarily regulating said source to change the voltage thereof, and speed regulating means for each motor comprising means for varying the re sistance inthe secondary of the motor with which it is associated, and a balance relay for controlling the operation of the resistance varying means having one coil responsive to the voltage of said source and an opposing coil responsive'to the voltage of the enerator driven b the motor. I [5 a. in combination, a plurality of induction motors having phase wound secondary windings,

variable resistance in the se ondary circuit at each motor, a source of electrical energy connected to the primary windings of said motors, a generator driven by each motor and adapted to deliver a voltage which varies directly with the speed thereof, means "for arbitrarily regulating said source to change the voltage thereof, and speed regulating means for each motor comprising means for varying the resistance in the secondary of the motor with which it is associated, and a balance relay for controlling the operation of the resistance varying means having one coil responsive to the voltage of said source and an opposing coil responsive to the voltage of the generator driven by the motor,

'8. In combination, induction motor having-a phase wound secondary winding, a variable resistance in the secondary circuit of said motor, a source oi electrical energy connected to the primary winding of said motor, means for arbitrarily regulating said source tochange an electrical condition of the energy supplied to said motor, and speed regulating means responsive to said electrical condition of the source for automatically varying said resistance so that the speed or" the motor is changed the same per cent as said electrical condition when the latter is changed.

'9. In combination, an induction motor having a phase wound secondary winding, a variable resistance in the secondary circuit of said motor, a source of electrical energy connected to the primary winding of said motor,.means for arbitrarily regulating said source to change an electrical condition of the energy supplied to said motor, and speed regulating means responsive to said electrical condition of the source for automatically varying said resistance so that the speed of the motor is maintained constant at a predetermined valuewhe'n said electrical condition of the source remains constant and so that the speed thereof is changed the same per cent as the electrical condition when the latter is changed.

10. In combination, an induction motor having a phase wound secondary winding,

a variable resistance in the secondary circuit of said motor, a source of electrical energy connected to the primary winding of said motor, means for arbitrarily regulating said source to change the voltage supplied to'said motor and speed regulating means responsive to the voltage of the murce for automatically varying said resistance so that the speed of the motor is changed the same per cent as said voltage when the latter is changed,

11. In combination, an induction motor having a phase wound secondary winding, variable resistance in the secondary circuit of said motor, source of electrical energy connected to primary winding of said motor, means for Jitrarily regulating said source to change the voltage supplied to said motor, and speed. regulating responsive .to the voltage of the source for automatically varying said resistance so that the speed of the motor is maintained constant at a predetermined value when the voltage of the source remains constantand so that the speed thereof is changed the same per cent as to voltage when the latter is changed.

12. In combination, an induction motor vhaving a phase wound secondary Windin a variable resistance in the secondary circuit of said motor, a source of electrical energy connected to the primary winding of said motor, a generator driven by said motor, means for arbitrarily regulating said source to change the voltage thereof, and

speed regulating means for said motor comprising means for varying said resistance, and a balance relay for controlling the operation of said resistance, varying means having one coil responsive to the voltage of said source and an opposing coil responsive to the voltage of the generator driven by the motor,

13. In combination, induction motor having a phase wound secondary winding, a variable resistance in the secondary circuit of said motor, a source of electrical energy connected to the primary Winding of said motor, a generator driven by said motor and adapted to deliver a voltage which varies directly with the speed thereof, means for arbitrarily regulating said source to change the voltage thereof, and speed regulating means for said motor comprising means for varying said resistance, and a balance relay for controlling the operation of said resistance varying means having one coil responsive to the voltage of said source and an opposing coil responsive to the voltage of the generator driven by the motor.

14. In combination with an. induction motor having a phase wound secondary winding, an alternating current generator adapted'to supply current to the primary Winding of said motor, means for operating said generator at different speeds to deliver currents at different frequencies to said motor, a variable resistance in the secondary circuit of said motor, and means for automatically varying said resistance to maintain a predetermined relation between the speed of said motor and'the synchronous speed thereof as the frequency of the current supplied thereto is varied.

15. In combination with an induction motor having aiphase wound secondary winding, an alternating current generator adapted to supply current to the primary winding of said motor, means for operating said generator at difi'erent speeds to-deliver currents at different frequencies to said motor, means for regulating said generator to deliver a voltage which varies with the frequency, a variable resistance in the secondary circuit of said motor, and means responsive to said voltage for automatically varying said resistance to maintain a predetermined relation between the speed of said motor and the synchronous speed thereof as the frequency of the current supplied thereto is varied. o

16. In combination with an induction motor having a phasewound secondary winding, an alternating current generator adapted to supply current to the primary winding of said motor, means for operating said" generator at different speeds to deliver currents at different frequencies to said motor, means for regulating ."said generator to deliver a voltage which varies with the frequency, a

- variable resistance in the secondary circuit of said motor, a generator driven by said motor and adapted to deliver a voltage which varies directly with the speed thereof, and speed regulating means for said motor comprising means for varying the amount of In witness whereof, I have hereunto set my hand this 7th day of August, 1919.

HARRY A. LAYCOOK. 

